Kill进程及重启EC2实例后MongoDB数据库消失，求排查方案

Hey there, this is a super common gotcha when manually starting MongoDB after an instance restart—let's figure out what's going on and get your data back.

What's Likely Happening #

The core issue here is almost certainly that you're starting MongoDB with the wrong data directory path when you run sudo mongod --dbpath ./db. Here's why:

• By default, MongoDB on most EC2 setups uses a system-level directory like /var/lib/mongodb (not a relative ./db folder in your current shell directory).
• When you restart your EC2 instance, your default SSH working directory might change, so ./db points to a brand-new empty folder instead of the one that held your actual data.

Step-by-Step Fix #

Let's walk through getting your data back:

1. Stop the current empty mongod instance first
   Run this command to shut down the process using the same dbpath you started with:

   sudo mongod --dbpath ./db --shutdown
   

   If that fails, find the process ID and kill it:

   ps aux | grep mongod
   sudo kill <your-mongod-pid>
   

2. Locate your actual MongoDB data directory
   There are two reliable ways to find this:

   • Check the MongoDB config file: Most systems store this at /etc/mongod.conf. Look for the dbPath field under the storage section:

     cat /etc/mongod.conf | grep -A 2 "storage"
     

     You should see something like:

     storage:
       dbPath: /var/lib/mongodb
     

   • Check MongoDB logs: If the config file isn't helpful, look for the dbpath in the system logs:

     sudo cat /var/log/mongodb/mongod.log | grep "dbpath"
     

     The log will have a line like dbpath=/var/lib/mongodb from previous successful starts.

3. Start MongoDB with the correct data path
   Use the path you found to start the daemon:

   sudo mongod --dbpath /var/lib/mongodb
   

   Pro tip: For future restarts, use the system service instead of manual commands—it'll automatically use the config file's settings:

   sudo systemctl start mongod
   

4. Verify your data is back
   Open the MongoDB shell and run show dbs—your filled databases should be visible again!

Prevent This From Happening Again #

• Avoid manual mongod starts: Use sudo systemctl start/stop/restart mongod instead. This ensures you're always using the configured data directory.
• Double-check relative paths: Never use ./db or other relative paths for critical data directories—always use absolute paths (like /var/lib/mongodb) if you have to start manually.
• Confirm your config: Periodically check /etc/mongod.conf to make sure the dbPath is set to the directory where your data lives.

内容的提问来源于stack exchange，提问作者cuuupid